Note: This is an article that appeared in the FAcilities Engineering Journal in the July/August 2014 Edition. You can visit the journal’s website at http://www.afe.org

A person walking across an insulative tile floor can build-up static electricity resulting in electrostatic discharges (ESD). When a hand touches a doorknob, it can take 3000 to 3500 volts to feel a sudden shock. In 1971, Intel’s 4004 microprocessor equaled about 2300 transistors. At the end of 2008, Intel’s Dual Core Itanium 2 smashed the 2 billion transistor equivalency barrier.

Both non-compliant and suspect counterfeit static control flooring have infiltrated the supply chain. Today, a very common practice by federal agencies is to require 3rd party certification of a static control floor installation before payment is issued. In order to prevent the potential bias of supplier self-certified testing, a 3rd party insures independent verification.

Figure 2

To insure proper selection and installation of static control flooring, there are several ESD flooring standards in place. U.S. Government agencies call out a 096XX designation for static resilient flooring. For instance, the DOT & FAA utilize 096536. The federal sector references ASTM F150 and ANSI/ESD LBS7.1[2] resistance testing for static control flooring protocols. So that everyone is on the same page, ASTM F150 defines:

A new installation shall have no individual reading greater than the stated limits defined in ESD DSTM7.1 or ASTM F150. In addition, the plant or facilities engineer should consider the following four testing methods.

Figure 3

1. Resistance:

The Resistance to a Groundable Point (RTG) and Point to Point (RPP) or Surface to Surface Test or Top to Top (RTT) resistance shall be between 2.5 x 104 ohms to <1.0 x 106 ohms for conductive flooring with a constant voltage (CV) of 10 volts and a RTG (Figure 3-Left) and RTT(Figure 3-Right) between 1.0 x 106 ohms to < 1.0 x 109 ohms for static dissipative flooring CV=100 volts).

Figure 4

2. Static Generation or Voltage in Combination with a Person (Figure 4) testing requires a result <300 volts for static control carpet when tested per AATCC-134-2011 (Electrostatic Propensity of Carpets) wearing conductive footwear. The ANSI/ESD STM97.2-2006 sets a requirement of <+/-100 volts. However, ANSI/ESD STM97.2 applies for all types of flooring and is not limited to carpets.

Figure 5

3. Resistance in combination with a person. ESD DSTM97.1-2013[3] measures the electrical system resistance of floor materials in combination with person wearing static control footwear which sets a limit of <3.5 x 107 ohms or <1.0 x 109 ohms depending on the method utilized. This test has not been listed on the federal list as a requirement. However, it is useful in determining resistance of a floor and a person wearing static control footwear such as shoes, heel grounders, ground strip booties (Figure 5, left) and temporary adhesive removal strips. This test method is often utilized for initial static control flooring qualification.

Figure 6

4. Electrostatic Decay (Static Decay): Current federal 096XX requirements incorrectly call out Fed-STD-101C/4046.1. This test method has been revised to Mil-STD-3010B, Method 4046 and should be conducted in a lab and not in the field where relative humidity cannot be controlled. This test is conducted using precut floor samples measuring 3-1/2” x 5-1/2” and clamped into the fixturing of an electrostatic decay testing system. The specimens are charged to +/-5000 volts and grounded to facilitate static decay to 0 volts for a limit of <0.25 seconds.

Figure 7

Before the measurement process takes place, grounding validation should be facilitated per ANSI/ESD S6.1-2009 (grounding). Connection to the electrical system insures that the floor is at the same potential as the facility.

Figure 8

It is critical to validate the ESD floor material before installation. For initial qualification, both ASTM F150 and ANSI/ESD S7.1 call out the use of scaled down prototype samples. In ASTM F150, a 48” x 48” sample (Figure 8) is used for conducting both RTG and RTT measurements. Securing a pre-made sample for initial testing from the static control floor manufacturing company can ultimately prevent a poor installation.

In past couple of years, the author received two (2) flooring company prototype specimens, both companies had failed ESD compliance testing. Consequently, these testing results led to reformulation of the product.

Non-compliant flooring can be attributed to the following:

ESD flooring system had not system grounding

Flooring adhesive was not conductive

Static Control flooring was unnecessarily coated leading to insulative readings

Formulation issues for tiles and epoxies flooring not in compliance with

ANSI/ESD S7.1 or ASTM F150

Improper selection of copper ground stripping

Improper test instrumentation used by Contractor or End-User

Knock off product

In an on-site experiment, a static dissipative floor produced a RTG and RTT reading below 1.0 x 109 ohms; the floor did not prevent ESD discharges from taking place. Thus, a special ESD event antenna peaked out at 2.7kV (see Figure 9) for several operators wearing insulative tennis shoes and walking over a static dissipative tile floor. Later, the test was repeated wearing ESD footwear and no ESD events were recorded.

In short, due to the significant investment required for static control flooring, dependence upon a supplier’s technical data sheet alone can prove costly! There is no substitute in not subjecting the floor to the following tests methods:

Grounding Validation

Resistance to a Groundable Point & Point to Point Resistance

Voltage in Combination with a Person wearing ESD Footwear

Resistance in Combination with a Static Control Floor and ESD Footwear

[1] Portions from 23 May 2011 at Keeping the Promise 2011 Veterans Conference and Apollo Expeditions to the Moon, edited by Edgar M. Cortright,